1. Field of the Invention
The present invention relates to non-uniformity correction of imagery collected by detector arrays. More particularly, the present invention relates to scene-base non-uniformity correction of imagery collected by scanning detector arrays.
2. Background Information
Imagery collected using infrared detectors (or sensors) must undergo non-uniformity correction (NUC) to remove fixed pattern noise (FPN) due to variations in pixel responsivity (gain) and pixel offset (level) of the detector. A standard technique for correcting FPN is by generating correction coefficients comprising gain and level terms for each detector element of a detector array based on a linear calibration using thermal reference (calibration) sources of known temperatures. This type of correction can remove FPN over a specific temperature range for a given period of time. However, this type of correction requires recalibration of the gain and level terms due to drift of the detector and changes in scene temperature. Such recalibration can be costly and time consuming.
To address these shortcomings, scene-based non-uniformity correction (SBNUC) techniques have emerged. Conventional SBNUC techniques may utilize repeated blurring of imagery collected from the scene. In this approach, the non-uniformity correction is based upon processing out-of-focus imagery to avoid memorization of high-frequency scene content by the non-uniformity correction routine. This approach, however, can interfere with an operator's (e.g., a pilot's) ability to consistently view a focused image of the scene.
Conventional SBNUC techniques may also utilize motion of the scene relative to the detector to distinguish FPN from details of the scene image. Because FPN remains in the same detector location while the scene moves, the FPN can be distinguishable from details of the scene. Such motion may be provided by the movement of a platform upon which the detector array is mounted (e.g., an air vehicle). Alternatively, such motion may be provided by “dithering” the detector array by a known amount using an appropriate dithering mechanism. Such dithering mechanisms are known to those skilled in the art. However, this dithering approach requires additional system complexity for dithering the detector array and requires additional processing of dithered image data.
It would be desirable to have a scene-based method and apparatus of compensating for FPN due to non-uniformity in the response of detector arrays that does not require repeated blurring of scene imagery, that does not require motion of an image relative to the detector array and that does not require complex dithering to achieve such motion. In addition, it would be desirable to have a scene-base approach that compensates for non-uniformity in the response of detector arrays that provides for improved performance over conventional methods of non-uniformity correction of FPN associated with detector arrays.